fevers

In article <30BBD164.634C at smartnet.net>, dwimmer at smartnet.net wrote:
> If I remember my immunology class right, it goes like this: When your
immune system is
> presented with a challenge, it produces some chemicals called pyrogens
(pyr=fire) which cause
> your body temperature to rise. Some bacteria contain pyrogenic
substances that they excrete or
> are released when they die. The reason your body likes to run a fever is
to make it a more
> hostile place for bacteria (they like 37dC not 39-40dC), your metabolism
is speeded up to fight
> infection faster, and it makes some other defenses more active. It has
been some time since I
> had all this, so it may not be quite right!
Basically all this is correct. On interaction with bacterial
lipopolysaccharide or other stimuli (like influenza virus) human
leukocytes release a substance called endogenous pyrogen. For a long time
it was thought that this was the cytokine interleukin (IL)-1, but other
pyrogenic cytokines (e.g. IL-6, Tumour Necrosis Factor, and Macrophage
Inflammatory Protein -1) have since been identified. These enter the
bloodstream and get transported to the brain where the cause localised
prostaglandin release, which causes an alteration to the body's thermal
set point (a bit like turning up the thermostat on a boiler) which results
in fever... amongst other symptoms (headache, muscle & joint aches, nausea
etc.). This is probably a host defence as some defences work better at
higher temperatures, but also viruses replicate more poorly (their
polymerases make more mistakes) at higher temperatures.
A good review on the whole subject is
Kluger, M.J. (1991) Fever: Role of Pyrogens and Cryogens. Physiological
Reviews 71, 93-127.
Hope this helps.
Graeme
--
Graeme Price
Microbial Molecular Genetics and Cell Biology Group,
School of Biological Sciences, Biology West Building,
University of Birmingham,
Edgbaston, Birmingham,
West Midlands, B15 2TT.
United Kingdom.
Tel. (+44) (0)121 414 6555
Fax. (+44) (0)121 414 6557
E-mail g.e.price at bham.ac.uk